Each of these three areas has been extensively developed in the last 30
years. Several books are written on each of these subjects and courses are available
through the academic institutions and the industry.
Most commercial CAD packages (software) consist of only a single
component: design or analysis or visualization. However, a few of the vendors have
developed an integrated package that includes not only these three areas, but also
includes the manufacturing software (CAM). Due to the large storage requirement,
integrated packages use either an UNIX workstation or a mainframe platform, and not
the popular PC platform. With the improvement in PC computing speed, it’s only a
matter of time before we see an integrated package run on a PC. CAD has
revolutionized the modern engineering practice; small and large companies use it alike,
spending several billion dollars for the initial purchase or lease alone. CAD related jobs
are high in demand and the new graduates have advantage over their senior colleagues,
as they are more up to date and more productive.
In this course, we will limit our coverage to the design only. Those of you
interested in analysis area, look into the course ME 160 – Introduction to Finite
Element Analysis.
Concurrent Engineering
Concurrent Engineering is another powerful CAD concept that has evolved in
the 90’s. According to this concept, there is an instantaneous communication between the
designer, analyst, and manufacturing. Changes made at any of these work centers are
immediately passed on to the others and the product is modified without delay. Often, the
customer, management, and the marketing people join in and become part of the process.
Concurrent engineering saves the valuable time and helps get the product out in the
market quicker. Products that use to take years from the date of its concept to the actual
production now take only a few weeks, and the final product is better and cost-effective.

Some large organizations have invested in Rapid Prototyping process. In this
process, the part is created by a CAD package and downloaded into the rapid prototyping
machine; the machine immediately manufactures the part, using a plastic material. This
is a good example of concurrent engineering, sometimes referred as Art to Part concept.
CAD Hardware
There are basically two types of devices that constitute CAD hardware: a)
Input devices, and b) Output devices. A brief description follows.
Input Devices
These are the devices that we use for communicating with computer, and
providing our input in the form of text and graphics. The text input is mainly provided
through keyboard. For graphic input, there are several devices available and used
according to the work environment. A brief description of these devices is given here.
Mouse: This is a potentiometric device, which contains several variable resistors that
send signals to the computer. The functions of a mouse include locating a point on the
screen, sketching, dragging an object, entering values, accepting a software command,
etc. Joystick and trackballs are analogous to a mouse device, and operate on the same
principle.
Digitizers: Digitizers are used to trace a sketch or other 2-D entities by moving a cursor
over a flat surface (which contains the sketch). The position of the cursor provides a
feedback to the computer connected with the device. There are electrical wires
embedded in orthogonal directions that receive and pass signals between the device and
the computer. The device is basically a free moving puck or pen shaped stylus,
connected to a tablet.
Light Pens: Lockheed’s CADAM software utilized this device to carry out the graphic
input. A light pen looks like a pen and contains a photocell, which emits an electronic
signal. When the pen is pointed at the monitor screen, it senses light, which is

converted to a signal. The signal is sent to the computer, for determination of the exact
location of the pen on the monitor screen.
Touch Sensitive Screens: This device is embedded in the monitor screens, usually, in the
form of an overlay. The screen senses the physical contact of the user. The new
generation of the Laptop computers is a good example of this device.
Other Graphic Input Devices: In addition to the devices described above, some CAD
software will accept input via Image Scanners, which can copy a drawing or schematic
with a camera and light beam assembly and convert it into a pictorial database.
The devices just described are, in general, independent of the CAD package being
used. All commercial CAD software packages contain the device drivers for the most
commonly used input devices. The device drivers facilitate a smooth interaction between
our input, the software, and the computer. An input device is evaluated on the basis of the
following factors:
•
Resolution
•
Accuracy
•
Repeatability
•
Linearity
Output Devices
After creating a CAD model, we often need a hard copy, using an output device.
Plotters and printers are used for this purpose. A plotter is often used to produce large
size drawings and assemblies, where as, a laser jet printer is adequate to provide a 3-D
view of a model. Most CAD software require a plotter for producing a shaded or a
rendered view.
CAD Software
CAD software is written in FORTRAN and C languages. FORTRAN provides the
number crunching, where as, C language provides the visual images. Early CAD
packages were turnkey systems, i.e., the CAD packages were sold as an integrated